Capacitive micromachined ultrasonic transducers (CMUTs) have been used for various applications for many years. However, there remain CMUT applications for which conventional CMUT approaches do not work well. One such application is operation in gas over a wide pressure range. The main difficulty with conventional CMUT operation over a large pressure range is that the CMUT plate will tend to be in contact with the substrate at the higher part of the pressure range, and not in contact with the substrate at lower pressures. CMUT performance depends significantly on whether or not the CMUT plate touches the substrate, so there will be significant (and undesirable) variation in device performance over the pressure range.
One conventional way to avoid this problem is to design the CMUT such that the CMUT plate does not touch the substrate at any part of the pressure range. However, this approach would undesirably lower device efficiency, especially at the low end of the pressure range.
Accordingly, it would be an advance in the art to provide improved CMUT performance over a wide pressure range.